Carbon-Nanotube Optics Designed for Space Telescopes

Photonics SpectraSep 2016
GREENBELT, Md., July 26, 2016 — A lightweight telescope that uses a carbon-nanotube mirror is being designed to fit easily inside a CubeSat, a NASA nanosatellite measuring four inches on one side. The telescope, which may be the first to carry a mirror made of carbon nanotubes in an epoxy resin, will be used for a range of CubeSat scientific investigations.

A team of scientists at NASA Goddard Space Flight Center has created a laboratory optical bench to test the telescope's overall design. The bench is comprised of three commercially available, miniaturized spectrometers optimized for the UV, visible and NIR wavelength bands. The spectrometers are connected via fiber optic cables to the focused beam of a three-inch-diameter carbon-nanotube mirror.

This laboratory breadboard is being used to test a conceptual telescope for use on CubeSat missions. Courtesy of NASA/
W. Hrybyk.
To make the mirror, a mixture of epoxy and carbon nanotubes is poured into a mold designed according to specification, and the mold is heated to cure and harden the epoxy. Once set, the mirror is coated with a reflective material of aluminum and silicon dioxide. After making a specific mandrel or mold, it can be used to produce many identical low-mass, highly uniform replicas at low cost.

"Complete telescope assemblies can be made this way, which is the team's main interest," said Peter Chen, president of Lightweight Telescopes Inc. “For the CubeSat program, this capability will enable many spacecraft to be equipped with identical optics and different detectors for a variety of experiments. They also can be flown in swarms and constellations."

In addition to being highly stable and easily reproducible, the carbon-nanotube mirrors do not require polishing.

John Kolasinski (left), Theodor Kostiuk (center) and Tilak Hewagama (right) hold mirrors made of carbon nanotubes in an epoxy resin. The mirror is being tested for potential use in a lightweight telescope specifically for CubeSat scientific investigations. Courtesy of NASA/W. Hrybyk.
The researchers have also demonstrated a way to integrate actuators into the optics at the time of fabrication. Electric fields are applied to the resin mixture before curing the mirror, causing the formation of carbon-nanotube chains. After curing, technicians can apply power to the mirror to deform the shape of the optical surface.

The optics technology being used to develop the CubeSat telescope may be applicable to larger telescopes comprised of multiple mirror segments, such as the James Webb Space Telescope or the twin telescopes at the Keck Observatory in Hawaii. Many of the mirror segments in these large telescopes are identical and could be produced using a single mold, eliminating the need to grind and polish individual segments to the same shape and focal length.

Scientist Theodor Kostiuk described the CubeSat telescope as an “exploratory tool for quick looks that could lead to larger missions.”

"This technology can potentially enable very-large-area technically active optics in space," Chen said. “No one has been able to make a mirror using a carbon-nanotube resin. This is a unique technology currently available only at Goddard. The technology is too new to fly in space, and first must go through the various levels of technological advancement. But this is what my Goddard colleagues (Kostiuk, Tilak Hewagama, and John Kolasinski) are trying to accomplish through the CubeSat program."

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